1. Field of the Invention
The present invention relates to a device for analyzing the function of a heart, having a measurement unit for generating a first measurement signal related to a first electrical or mechanical heart variable, and an evaluation unit for evaluating the measurement signal.
2. Description of the Prior Art
In the monitoring, diagnosis and treatment of heart diseases or other changes in a heart, accurate determination of the heart's current condition, with minimal risk of erroneous interpretations, is important. Automatic monitoring of the heart is valuable so therapeutic measures can be instituted without delay when needed.
There are numerous heart variables, both electrical and mechanical, such as the electrocardiographic (ECG) signal, the heart's impedance, blood pressure, blood volume, blood flow, heart sounds and movements of the heart walls, which reflect the heart's function. The sensing of any of these variables to obtain a measurement signal which can be evaluated in establishing the condition of the heart is known in the art.
One way to graphically elucidate the electrocardiogram by plotting the voltage of a recorded electrocardiogram against the time derivative of the voltage is described in an article 30 entitled "Phase Plane Plot of Electrograms as a Marker of Ventricular Electrical Instability During Acute Ischemia: Initial Experimental Results and Potential Clinical Applications", published in the journal PACE, Vol. 15, Part II, November 1992, pp. 2188-2193. This procedure produces a curve equivalent to the recorded ECG signal. The article shows that there is a relationship between changes in parts of the curve during acute ischemia and development of ventricular fibrillation. The authors of the article state that a presentation of an electrocardiogram in graphical form can be an excellent complement to traditional real-time presentation.
U.S. Pat. No. 4,417,306 describes an apparatus which monitors and stores heart signals. The apparatus senses the ECG, and the ECG signal 5 must have a predetermined slope, amplitude, duration and course to be accepted as a heart beat. The QRS complex is the main segment sensed, i.e. the electrical signals occurring in the heart when there is a ventricular beat (ventricular systole).
U.S. Pat. No. 4,453,551 describes an apparatus designed to detect ventricular fibrillation (VF). The apparatus senses the ECG signal from the heart, digitizes the sensed signal, and amplifies the digital signal to a predetermined peak amplitude. The amplified signal can then be analyzed in different ways to ascertain whether or not VF is present. For example, the statistical distribution of gradients or the frequency of the maximum negative gradient can be analyzed.
European Application 0 220 916 describes an apparatus designed to detect the presence of ventricular tachycardia (VT) and VF and to supply treatment terminating these conditions. The apparatus senses the heart's ECG at a plurality of points in the heart and determines the sequence in which the signals are detected at the different measurement points. In VT and VF, the detected sequence deviates from the normal sequence in different ways.